A conventional turret punch press performs punching and press working by using punches and dies.
In the meantime, due to increasing diversity and complexity in the shapes of workpieces in recent years, there is a growing demand for performing not only various types of punching but also various types of tapping on works by use of a single turret punch press.
The above-mentioned technique has been disclosed in Patent Document 1 and Patent Document 2, for example.
Incidentally, in a conventional turret punch press, mounting sections (mounting sections for tools) provided to a turret are designed as mounting sections dedicated for punches or mounting sections dedicated for tapping tools, and the punching tools and the tapping tools are mounted on the mounting sections of the respective types. Accordingly, the mounting section for tapping tool is used exclusively for the tapping tools and it is therefore not possible to mount any punching tools on the mounting section for tapping tool even in the case of a process using no tapping tools. Accordingly, there is a problem of a decrease in the types of tools to be loaded on the turret, which leads to a difficulty in handling various processes with a single turret punch press.
Meanwhile, to be specific, tapping on a plate-shaped workpiece may be performed by subjecting the workpiece to punching to form pilot holes having small diameters in the workpiece and then performing tapping either directly on the pilot holes or after subjecting the pilot holes to burring. Therefore, a punch press includes: a tap tool with a tap provided thereto rotatably and vertically movably for performing tapping. A tap die used in cooperation with the tap tool is given at a position below this tapping tool.
The above-mentioned technique has been disclosed in Patent Document 3, for example.
A tap die disclosed in Patent Document 3 has a configuration as shown in FIG. 1. Specifically, a tap die 505 to be used in cooperation with a tap tool 503, which is used by being mounted on a punch holder 501 such as an upper turret in a turret punch press, is detachably replaceably provided in a die holder 507 such as a lower turret in the punch press. The tap die 505 includes a cylindrical die body 509. An inner cylinder 515 is provided vertically movably inside this die body 509. The inner cylinder 515 has a tap contact member 513 located on an upper part thereof and pressed downward by a tap 511 being rotatably and vertically movably provided to the tap tool 103.
The inner cylinder 515 is always biased upward by means of coil springs 517, whereby an upper surface of this inner cylinder 515 is in contact with a lower surface of an inner flange 509F provided on an upper part of the die body 509. Further, a circumferential groove 521 capable of being communicatively connected to and disconnected from an air supply port 519 provided in the die body 509 is formed in an outer circumferential surface of the inner cylinder 515. This circumferential groove 521 communicates with the inside of the inner cylinder 515.
The air supply port 519 in the die body 509 is connected to an air source 523 via a connecting path 525. A pressure switch 527 for detecting whether the air supply port 519 and the circumferential groove 521 are in a communicatively connected state or disconnected state is connected to this connecting path 525.
Therefore, tapping is performed on a pilot hole WH in a workpiece W by: positioning the pilot hole WH formed in the workpiece W on the die body 509 in the tap die 505; bringing the tap tool 503 downward by use of a ram (a striker) vertically movably provided to the punch press; pressing and fixing the workpiece W onto the die body 509; bringing the tap 511 relatively downward; and rotating the tap 511.
Thereafter, as a lower end (a tip end) of the tap 511 comes into contact with the tap contact member 513 and lowers the inner cylinder 515 against a biasing force of the coil springs 517, the air supply port 519 is connected to the circumferential groove 521. Therefore, an air pressure inside the connecting path 525 is changed from a high pressure to a low pressure as the air supply port 519 previously in the communicatively disconnected state is connected to the circumferential groove 521, and it is hence possible to detect this change in air pressure by use of the pressure switch 527. Accordingly, when the tap 511 moves up after descending from a lifted position to the lowest descending position, it is possible to detect fracture and the like of the tap 511, for example, by detecting whether or not the pressure switch 527 repeats ON-OFF-ON operations.
However, in the above-described configuration, when a tap tool provided with a tap having a large diameter is erroneously mounted as the tap tool 503 to be mounted on the punch holder 501 in the punch press instead of the tap tool 503 provided with the tap 511 having the small diameter, a stroke length of the tap having the large diameter and a large screw pitch becomes greater even when the number of revolutions of the tap is the same. Accordingly, the tap is apt to lower the inner cylinder 515 after the inner cylinder 515 reaches a descending end, for example. This leads to a problem of causing fracture of the tap, damage on the tap tool, or the like.
Meanwhile, the above-described conventional configuration also has a problem that long chips being generated at the time of tapping may twine around the tap contact member, a problem that part of chips may enter a gap between the upper surface of the inner cylinder 515 and the inner flange 509F of the die body 509, and some other problems.